Single-crystal vibrational spectra of tetragonal and orthorhombic lead monoxide

Abstract

All the fundamental modes of vibration of tetragonal PbO have been observed and all but one assigned unequivocally by single-crystal techniques: B1g 338.7, A1g 146.5, Eg 321.5 and 81.0, A2u 116, and Eu 243 cm–1. From the i.r. longitudinal and transverse optic (LO and TO) frequencies, the principal components of the dielectric tensor are estimated to be ε1= 20.3 and ε3= 11.9. The first complete Raman spectrum, and single-crystal i.r. reflectance data, are reported for orthorhombic (yellow) PbO. The assignment has been partially established for the Raman spectrum with the aid of the group-theoretical prediction, based on a line-group approach, that i.r. and Raman modes should be in near coincidence. The high dielectric constant of the material has been accounted for, a principal contribution coming from the single B1u mode (normal to the plane of the PbO chains) which is of unusual breadth.